1. Field of the Invention
This invention relates to a device intended for the taking of samples and/or injection inside sealed receptacles such as e.g. test tubes sealed with plastic stoppers.
2. Description of the Prior Art
Generally, it is known that for security and precision purposes, numerous analysis processes and especially in biological processes, we use sample tubes plugged with rubber (or more generally plastomer) bungs, in order to be able to perform all manipulations pertaining to these processes without having to remove the stopper and therefore without direct access to the sample. In the case of hematological analyses, increasingly frequent use is made of sealed test tubes in which a relative vacuum is created enabling the use of a syringe to be avoided when taking a blood sample, the blood being directly drawn into the tube under the effect of the depression.
The taking of samples and/or injections performed into these tubes then entails the use of devices each comprising a hollow needle connected to a suction and/or delivery pipe.
When it equips an automated analysis system, the sampling device is borne by a pipeting head equipped with means ensuring vertical displacement of the needle, and possibly mobile above a pipeting area in which a plurality of sample tubes is arranged. It is obvious that in this case the needle must be capable of performing a multiplicity of piercings and samplings without the precision of the device being affected.
In practice it transpires that the perfecting of such a device and the design of such sampling needles give rise to numerous problems.
Thus, the use of conventional hollow needles with substantially cone-shaped tapered tips is not really suitable for automated or semi-automated analysis systems for the following reasons:
during piercing of the stopper, these needles perform like hollow punches, cutting out in the stopper a circular portion of cross-section substantially equal to the cross-section of the needle channel: this circular portion engages in the channel and causes at least partial obturation thereof. Accordingly, during the suction phase, this portion generates a more or less considerable loss of head that constitutes a first source of error on the quantities sampled off (which must be constant for each sampling); PA1 during the piercing action, the stopper is subjected to a deformation causing a pressure variation (excess pressure) inside the receptacle, said variation constituting a second source of error concerning the quantities sampled off. Likewise, during extraction of the needle, the deformation of the stopper in the opposite direction generates a depression which brings about a suction effect tending to aspirate the liquid sampled off. The imprecision resulting from these two phenomena is amplified by the fact that the level of the sample inside the tube is variable from one tube to another and that, therefore, the values of the excess pressure and depression cannot be determined; PA1 The hollow punch effect leads to the formation of bores that close up poorly after extraction of the needle, as a result of which the tightness of the seal can no longer be guaranteed.
In order to remedy the problems pertaining to the imprecision of the quantities sampled off, it has been proposed that use be made of sampling devices using electrovalve sets enabling the performance of complex sampling sequences taking into account the above-mentioned parameters. However, this solution has proved costly, not very reliable and yet does not solve all the above-mentioned drawbacks.